Piezoelectric vibrating reed, piezoelectric vibrating reed manufacturing method, piezoelectric vibrator, oscillator, electronic device and radio timepiece

ABSTRACT

An electrode forming step of forming a pair of electrodes by patterning an electrode film on an outer surface of a piezoelectric plate includes: an electrode film forming step of forming the electrode film; a photoresist film forming step of forming a photoresist film on the electrode film; a first exposure step of exposing the photoresist film through a mask; and a second exposure step of further exposing the photoresist film through a correction mask on which a second opening is disposed at a position overlapping with a part of the first opening. An opening width of the second opening corresponding to a clearance between the pair of electrodes is equal to or less than an opening width of the first opening corresponding to the clearance.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2011-038832 filed on Feb. 24, 2011, the entire content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a manufacturing method of a piezoelectric vibrating reed that is made of a piezoelectric material, such as quartz or lithium tantalate, a piezoelectric vibrating reed that is manufactured by this manufacturing method, a piezoelectric vibrator having the piezoelectric vibrating reed, and an oscillator, an electronic device and a radio timepiece that have the piezoelectric vibrator.

2. Description of the Related Art

In recent years, mobile telephones and portable information terminal devices employ a piezoelectric vibrator that uses crystal or the like as a time source, a timing source of control signals and a reference signal source etc. As this type of piezoelectric vibrator, various piezoelectric vibrators are provided. As one of them, a piezoelectric vibrator that includes a tuning fork type piezoelectric vibrating reed is known. This piezoelectric vibrating reed is a vibrating reed that causes a pair of vibrating arm portions that are arranged in parallel with each other to vibrate at a predetermined resonance frequency in a direction to move closer to or away from each other.

In recent years, miniaturization of various electronic devices that incorporate a piezoelectric vibrator is promoted, as represented by mobile phones. Therefore, the piezoelectric vibrating reed included in the piezoelectric vibrator is also required to be more miniaturized. To address this, it is expected that the entire length of the piezoelectric vibrating reed is shortened by shortening the length of the vibrating arm portions or by shortening the length of a base portion.

However, when the entire length of the piezoelectric vibrating reed is shortened by shortening the length of the base portion, mounting performance deteriorates. In addition, vibration of the vibrating arm portions is likely to become unstable and vibration leakage (leakage of vibration energy) is likely to occur through the base portion. As a result, there is a possibility of an increase in a crystal impedance (CI) value.

To address this, in order to promote miniaturization by shortening the entire length of the piezoelectric vibrating reed, it is effective to shorten the length of the vibrating arm portions rather than the base portion. However, when the length of the vibrating arm portions is shortened, an R1 value (a series resonance resistance value) increases and vibration characteristics tend to deteriorate. Particularly, the R1 value is proportional to an effective resistance value Re. Therefore, if the R1 value becomes higher, it becomes difficult to operate the piezoelectric vibrating reed at low power.

To address this, in order to reduce the R1 value, it is known that groove portions are respectively formed on both principal surfaces (i.e., top and back surfaces) of the vibrating arm portions, along a longitudinal direction of the vibrating arm portions (refer to JP-A-2004-120556).

This piezoelectric vibrating reed is formed such that the pair of vibrating arm portions each have an H-shaped cross section due to the groove portions, and a pair of excitation electrodes face each other fully. Therefore, as compared to a case in which the groove portions are not formed, an electric field operates more efficiently and it is possible to reduce vibration loss. It is therefore possible to improve the vibration characteristics and it is also possible to suppress the R1 value to a low value.

In this way, in order to promote miniaturization of the piezoelectric vibrating reed while suppressing the increase of the R1 value, it is effective to shorten the length of the vibrating arm portions while forming the groove portions in the vibrating arm portions.

This type of excitation electrode is made of for example, Au, Cr or the like and the electrodes are arranged to be separated from each other at a certain interval. This arrangement is formed by a photolithography technique using a photoresist. In a manufacturing step performed by the photolithography technique, a metal film is disposed on the surfaces of the pair of vibrating arm portions by sputtering or the like, a photoresist film is disposed on the metal film, and a photoresist pattern is formed by exposure via a mask. Then, etching is performed using the photoresist pattern as a mask and the pair of excitation electrodes are thereby formed.

A resist for the photoresist film is made of resin or the like that has fluidity and photosensitivity to ultraviolet light. Therefore, it is difficult to uniformly coat the resist on the surfaces of the pair of vibrating arm portions. Therefore, when a photoresist film 201 is locally thicker (an A portion) as shown in FIG. 27A, a bottom surface 202 is not exposed at a time of exposure, as shown in FIG. 27B. As a result, the photoresist film 201 is left (a B portion) after development, as shown in FIG. 27C. If etching processing is performed in this state, a pair of the excitation electrodes are formed such that they are connected, resulting in a short circuit of the electrodes.

To address this, in order to form a uniform surface, a method is also known in which an exposure time is increased at the time of exposure so that a thick portion is removed sufficiently. Further, a method is proposed in which laser is irradiated onto the formed photoresist pattern and the shape of at least part of the pattern is thereby adjusted (refer to JP-A-2003-133875).

SUMMARY OF THE INVENTION

However, with the above-described known manufacturing method (in which the exposure time is increased), as shown in FIGS. 28A-28C, a region (a C portion), in which the photoresist film 201 is formed such that its thickness is in a normal range, is removed with a removal width L2 that is wider than an original removal width L1. In other words, a removal amount is excessive and a pattern dimension is smaller than a desired value. As a result, characteristic values are affected, such as an increase in the R1 value. Further, in the manufacturing method described in JP-A-2003-133875, a laser is irradiated onto uneven portions one by one after a development step, resulting in an increase in both costs and time.

The invention has been made in light of the above-described circumstances, and provides a piezoelectric vibrating reed manufacturing method that can suppress a short circuit failure between electrodes without increasing a resistance value R1, a piezoelectric vibrating reed that is manufactured by this manufacturing method, a piezoelectric vibrator having the piezoelectric vibrating reed, and an oscillator, an electronic device and a radio timepiece that have the piezoelectric vibrator.

In order to solve the above-described problems, the invention adopts the following method.

A piezoelectric vibrating reed manufacturing method according to the invention is a method for manufacturing a piezoelectric vibrating reed using a wafer made of a piezoelectric material. The piezoelectric vibrating reed manufacturing method includes the steps of: forming an outer shape of a piezoelectric plate by etching the wafer using a photolithography technique; and forming a pair of electrodes by patterning an electrode film on an outer surface of the piezoelectric plate. The electrode forming step includes: an electrode film forming step of forming the electrode film on a surface of the piezoelectric plate; a photoresist film forming step of forming a photoresist film on the electrode film; a first exposure step of exposing the photoresist film through a mask on which a first opening is disposed for a photoresist pattern; and a second exposure step of further exposing the photoresist film through a correction mask on which a second opening is disposed at a position overlapping with a part of the first opening. An opening width of the second opening corresponding to a clearance between the pair of electrodes is equal to or less than an opening width of the first opening corresponding to the clearance.

In the piezoelectric vibrating reed manufacturing method according to the invention, even if the thickness of the photoresist film formed in the photoresist film forming step becomes uneven and there is a section where the photoresist film is not sufficiently removed in the first exposure step, the opening width of the second opening is equal to or less than the opening width of the first opening Therefore it is possible to sufficiently remove the photoresist film to be removed by the second exposure step without reducing a surface area of the photoresist film to be left. Accordingly, it is possible to inhibit a short circuit failure between the pair of electrodes.

Further, with the piezoelectric vibrating reed manufacturing method according to the invention, in the outer shape forming step, the outer shape of the piezoelectric plate is formed such that the piezoelectric plate includes a pair of vibrating arm portions disposed in parallel with each other, a base portion that integrally fixes the pair of vibrating arm portions, and elongated groove portions that are formed on principal surfaces of the pair of vibrating arm portions and extend from base end portions of the vibrating arm portions toward tip end portions. The pair of electrodes include principal surface electrode portions formed in the groove portions and side surface electrode portions formed on side surfaces of the vibrating arm portions. The clearance between the pair of electrodes is a clearance between the principal surface electrode portion and the side surface electrode portion.

Generally, the interval between the groove portions and the side surfaces of the vibrating arm portions in the piezoelectric vibrating reed is formed to be significantly narrow in order to suppress the R1 value to a low value. Therefore, the clearance between the principle surface electrode portion formed in each of the groove portions and the side surface electrode portion formed in each of the side surfaces of the vibrating arm portions becomes very narrow.

In the piezoelectric vibrating reed manufacturing method according to the invention, the second opening is disposed in a region corresponding to the clearance between the principal surface electrode portion and the side surface electrode portion. Therefore, it is possible to reliably remove the photoresist film of the clearance by the second exposure step. Thus, it is possible to reliably inhibit a short circuit failure between the principal surface electrode portion and the side surface electrode portion in the clearance.

Further, in the piezoelectric vibrating reed manufacturing method according to the invention, the opening width of the second opening is equal to or more than 0.6 times and equal to or less than 0.7 times the opening width of the first opening.

In the piezoelectric vibrating reed manufacturing method according to the invention, it is possible to secure a more favorable clearance to inhibit a short circuit failure between each of the electrodes.

Moreover, in the piezoelectric vibrating reed manufacturing method according to the invention, in the outer shape forming step, the outer shape of the piezoelectric plate is formed such that the piezoelectric plate includes a pair of vibrating arm portions disposed in parallel with each other, and a base portion that integrally fixes the pair of vibrating arm portions. The opening width of the first opening is substantially the same as the opening width of the second opening in a region corresponding to a fork portion of the pair of vibrating arm portions.

In the vicinity of the fork portion, even if the removal amount of the electrode film becomes excessive, it does not affect characteristic values, more specifically, it does not increase the R1 value. Given this, if the opening width of the first opening is made substantially the same as the opening width of the second opening and the photoresist film of the clearance is removed, it is possible to more reliably inhibit a short circuit failure between the electrodes.

With a piezoelectric vibrating reed which is manufactured by the piezoelectric vibrating reed manufacturing method, it is possible to favorably suppress a short circuit between the electrodes.

A piezoelectric vibrator according to the invention includes the above-described piezoelectric vibrating reed according to the invention.

The piezoelectric vibrator according to the invention includes the piezoelectric vibrating reed which is unlikely to cause a short circuit between the electrodes and provides reliability for stable operation. It is therefore possible to achieve a high-quality piezoelectric vibrator having improved reliability.

An oscillator according to the invention has a feature in that the above-described piezoelectric vibrator according to the invention is electrically connected to an integrated circuit, as an oscillation element.

An electronic device according to the invention has a feature in that the above-described piezoelectric vibrator according to the invention is electrically connected to a time measuring portion.

A radio timepiece according to the invention has a feature in that the above-described piezoelectric vibrator according to the invention is electrically connected to a filter portion.

The oscillator, the electronic device and the radio timepiece according to the invention include the above-described piezoelectric vibrator. Therefore, similarly, it is possible to improve reliability and achieve higher quality.

According to the invention, it is possible to suppress a short circuit failure without increasing the resistance value R1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view showing an embodiment of a piezoelectric vibrating reed according to the invention;

FIG. 2 is an enlarged view of the piezoelectric vibrating reed shown in FIG. 1, which is enlarged around base end portions of vibrating arm portions;

FIG. 3 is a cross-sectional view of the piezoelectric vibrating reed taken along a line A-A shown in FIG. 2;

FIG. 4 is a flowchart when the piezoelectric vibrating reed shown in FIG. 1 is manufactured;

FIG. 5 is a diagram showing a step when the piezoelectric vibrating reed shown in FIG. 1 is manufactured, and shows a state in which an etching protection film is formed on both surfaces of a wafer;

FIG. 6 is a diagram showing a state in which the etching protection film is patterned in accordance with an outer shape of piezoelectric plates of the piezoelectric vibrating reeds, from the state shown in FIG. 5;

FIG. 7 is a view in the direction of arrows taken along a line B-B shown in FIG. 6;

FIG. 8 is a diagram showing a state in which the wafer is etched using the etching protection film as a mask, from the state shown in FIG. 7;

FIG. 9 is a diagram showing a state in which the etching protection film is further patterned, from the state shown in FIG. 8;

FIG. 10 is a diagram showing a state in which the wafer is etched using the etching protection film that has been patterned again, as a mask, from the state shown in FIG. 9;

FIG. 11 is a diagram showing a state in which an electrode film is formed, from the state shown in FIG. 10;

FIG. 12 is a plan view showing a mask that is used in a first exposure step after a photoresist film is coated on the electrode film from the state shown in FIG. 11;

FIG. 13 is a plan view showing a correction mask that is used further in a second exposure step after completion of the first exposure step;

FIG. 14 is a diagram showing a state in which the photoresist film is formed on the electrode film and the photoresist film is patterned, from the state shown in FIG. 11;

FIG. 15 is a diagram showing a state in which the patterned photoresist film is used as a mask and the electrode film is etched, from the state shown in FIG. 14;

FIGS. 16A-16D are diagrams showing states of an electrode forming step according to the invention;

FIG. 17 is an external view showing an embodiment of a piezoelectric vibrator according to the invention;

FIG. 18 is an internal structural diagram of the piezoelectric vibrator shown in FIG. 17, and shows the piezoelectric vibrating reed from above with a lid substrate removed;

FIG. 19 is a cross-sectional view of the piezoelectric vibrator taken along a line D-D shown in FIG. 18;

FIG. 20 is an exploded perspective view of the piezoelectric vibrator shown in FIG. 19;

FIG. 21 is a structural diagram showing an embodiment of an oscillator according to the invention;

FIG. 22 is a structural diagram showing an embodiment of an electronic device according to the invention;

FIG. 23 is a structural view showing an embodiment of a radio timepiece according to the invention;

FIG. 24 is an external perspective view showing an AT-cut piezoelectric vibrating reed;

FIG. 25 is a plan view showing a mask that is used in the first exposure step when the piezoelectric vibrating reed shown in FIG. 24 is manufactured;

FIG. 26 is a plan view showing a correction mask that is used in the second exposure step after the mask shown in FIG. 25 is used;

FIGS. 27A-27C are diagrams showing states of an electrode forming step in a piezoelectric vibrating reed manufacturing method according to a related art; and

FIGS. 28A-28C are diagrams showing states of an electrode forming step in a piezoelectric vibrating reed manufacturing method that is performed in the related art in order to improve the states shown in FIG. 27.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Piezoelectric Vibrating Reed

Hereinafter, an embodiment of a piezoelectric vibrating reed according to the invention will be explained with reference to FIG. 1 to FIG. 16.

A piezoelectric vibrating reed 1 of the present embodiment is incorporated into a glass-packaged or cylinder-packaged piezoelectric vibrator of a surface-mounting type, for example. As shown in FIG. 1 and FIG. 2, the piezoelectric vibrating reed 1 includes a tuning-fork type piezoelectric plate 2 made of a piezoelectric material, such as quartz, lithium tantalate or lithium niobate.

Note that FIG. 1 is a plan view of a top surface side of the piezoelectric vibrating reed 1. FIG. 2 is an enlarged view around base end portions of vibrating arm portions 3 and 4 shown in FIG. 1.

The piezoelectric plate 2 is provided with the pair of vibrating arm portions 3 and 4 that are arranged in parallel with each other, and a base portion 5 that integrally fixes the base end portions of the pair of vibrating arm portions 3 and 4. Further, groove portions 6 are formed in principal surfaces (top and back surfaces) of the pair of vibrating arm portions 3 and 4, and extend from the base end portions of the vibrating arm portions 3 and 4 towards tip end portions thereof. The groove portions 6 have a constant width and are elongated in the direction of the vibrating arm portions 3 and 4. The groove portions 6 are formed to extend from the base end portions of the vibrating arm portions 3 and 4 to positions over intermediate portions of the vibrating arm portions 3 and 4. With this structure, the pair of vibrating arm portions 3 and 4 each have an H-shaped cross section as shown in FIG. 3.

Note that FIG. 3 is a cross-sectional view taken along a line A-A shown in FIG. 2.

On an outer surface of the piezoelectric plate 2 formed in this manner, a pair of excitation electrodes 10 and 11 and a pair of mount electrodes 12 and 13 are formed with a fork portion 15 interposed therebetween, as shown in FIG. 1 and FIG. 2. Among them, the pair of excitation electrodes 10 and 11 are electrodes that allow the pair of vibrating arm portions 3 and 4 to vibrate at a predetermined resonance frequency in a direction to move closer to or away from each other when a voltage is applied. The excitation electrodes 10 and 11 are formed mainly on outer surfaces of the pair of vibrating arm portions 3 and 4, respectively, by patterning in an electrically isolated state.

Specifically, as shown in FIG. 3, the one excitation electrode 10 is mainly formed in the groove portion 6 of the one vibrating arm portion 3 and on side surfaces of the other vibrating arm portion 4. The other excitation electrode 11 is mainly formed on side surfaces of the one vibrating arm portion 3 and in the groove portion 6 of the other vibrating arm portion 4.

Here, the excitation electrodes 10 and 11 will be explained in more detail.

As shown in FIG. 1 to FIG. 3, the excitation electrodes 10 and 11 of the present embodiment each include principal surface electrode portions 20, side surface electrode portions 21, and a connection electrode portion 22.

The principal surface electrode portions 20 are electrodes that are formed in the groove portions 6 and on the principal surfaces of the vibrating arm portions 3 and 4 that encompass the groove portions 6. The side surface electrode portions 21 are electrodes that are formed on the side surfaces of the vibrating arm portions 3 and 4 and on the principal surfaces of the vibrating arm portions 3 and 4 that are connected to the side surfaces. In this case, as shown in FIG. 1, the side surface electrode portions 21 formed on the inner side surfaces (on the fork portion 15 side) of the vibrating arm portions 3 and 4, and the side surface electrode portions 21 formed on the outer side surfaces of the vibrating arm portions 3 and 4 are electrically connected through the connection electrode portion 22 formed to be closer to the tip end portions than the groove portions 6.

As shown in FIG. 3, the principal surface electrode portions 20 and the side surface electrode portions 21 are arranged to be separated from each other by providing a clearance W0 that is a fixed clearance to avoid short circuits. The clearance W0 is a very small clearance of 15 μm, for example. Since the clearance W0 is accurately formed in this manner, it is possible to inhibit short circuits and the like between the principal surface electrode portions 20 and the side surface electrode portions 21. On the other hand, in the vicinity of the fork portion 15, the side surface electrode portion 21 that is formed on the inner side surface of the one vibrating arm portion 3 and the side surface electrode portion 21 that is formed on the inner side surface of the other vibrating arm portion 4 are arranged to be separated from each other by providing a clearance U0 that corresponds to the width of the fork portion 15.

As shown in FIG. 2 and FIG. 3, the connection electrode portion 22 is an electrode that is formed on the principal surface of the one vibrating arm portion 3 so as to be connected to the side surface electrode portions 21. The connection electrode portion 22 is also connected to the principal surface electrode portions 20 formed on the vibrating arm portion 4 after being led out towards the vibrating arm portion 4 on the top surface side via the principal surface of the base portion 5.

By the connection electrode portion 22, the principal surface electrode portion 20 disposed on the one vibrating arm portion 3 and the side surface electrode portion 21 disposed on the other vibrating arm portion 4 are connected on the top surface side. Moreover, the side surface electrode portion 21 disposed on the one vibrating arm portion 3 and the principal surface electrode portion 20 disposed on the other vibrating arm portion 4 are connected on the back surface side.

Note that, although FIG. 1 and FIG. 2 illustrate the top surface side of the piezoelectric vibrating reed 1, an electrode pattern on the back surface side is symmetrical to an electrode pattern on the top surface side.

As shown in FIG. 2, the pair of mount electrodes 12 and 13 are formed on an outer surface including the principal surface and side surfaces of the base portion 5, and are electrically connected to the pair of excitation electrodes 10 and 11, respectively, via a lead-out electrode 16. Therefore, a voltage is applied to the pair of excitation electrodes 10 and 11 via the mount electrodes 12 and 13.

Note that the excitation electrodes 10 and 11, the mount electrodes 12 and 13 and the lead-out electrode 16 are laminated films of chromium (Cr) and gold (Au), for example, and are obtained by forming a chromium film, which has good adhesion to crystal, as a base and then forming a thin gold film on the surface. However, they are not limited to this case. For example, a thin gold film may be further laminated on the surface of a laminated film made of chromium and nichrome (NiCr), or a single film made of chromium, nickel, aluminum (Al), titanium (Ti) or the like may also be used.

In addition, a weight metal film 17 (which includes a rough adjustment film 17 a and a fine adjustment film 17 b) is formed on the tip end portions of the pair of vibrating arm portions 3 and 4 as shown in FIG. 1, in order to perform adjustment (frequency adjustment) of their vibration state such that the pair of vibrating arm portions 3 and 4 vibrate within a predetermined frequency range. By performing frequency adjustment using the weight metal film 17, the frequency of the pair of vibrating arm portions 3 and 4 can be set to fall within a nominal frequency range of a device.

When the piezoelectric vibrating reed 1 structured in this manner is operated, a predetermined drive voltage is applied between the pair of excitation electrodes 10 and 11 and a current is allowed to flow. By doing so, the pair of vibrating arm portions 3 and 4 are allowed to vibrate at a predetermined frequency in a direction to move closer to or away from each other. This vibration can be used as a time source, a timing source of control signals, a reference signal source, and the like.

Piezoelectric Vibrating Reed Manufacturing Method

Next, a method for manufacturing the above-described piezoelectric vibrating reed 1 using a wafer made of a piezoelectric material will be explained with reference to a flowchart shown in FIG. 4.

First, a wafer S is prepared that has been subjected to polishing and finished highly accurately to a predetermined thickness (S1). Subsequently, an outer shape forming step is performed in which the wafer S is etched by a photolithography technique to form an outer shape of a plurality of the piezoelectric plates 2 on the wafer S (S2). This step will be explained specifically.

First, as shown in FIG. 5, an etching protection film 30 is formed on both surfaces of the wafer S (S2 a). For example, a film of chromium (Cr) having a thickness of several μm is formed as the etching protection film 30. Subsequently, a photoresist film (not shown in the drawings) is patterned on the etching protection film 30 by a photolithography technique. At this time, the photoresist film is patterned so as to surround the periphery of each of the piezoelectric plates 2 including the pair of vibrating arm portions 3 and 4 and the base portion 5. Then, etching is performed using the photoresist film as a mask, and unmasked regions of the etching protection film 30 are selectively removed. Then, the photoresist film is removed after the etching.

In this way, as shown in FIG. 6 and FIG. 7, the etching protection film 30 can be patterned along the outer shape of the piezoelectric plates 2, namely, outer shapes of the pair of vibrating arm portions 3 and 4 and the base portion 5 (S2 b). At this time, patterning is performed for the number of the plurality of piezoelectric plates 2. Note that FIG. 7 to FIG. 10 are diagrams showing cross sections taken along a line B-B shown in FIG. 6.

Next, both the surfaces of the wafer S are respectively etched using the patterned etching protection film 30 as a mask (S2 c). In this way, as shown in FIG. 8, the regions that are not masked by the etching protection film 30 are selectively removed, and the outer shape of the piezoelectric plates 2 can be formed. The outer shape forming step (S2) ends at this point in time.

Subsequently, a groove forming step is performed in which the groove portions 6 are formed on the principal surfaces of the pair of vibrating arm portions 3 and 4 (S3). Specifically, similarly to the outer shape forming step described above, a photoresist film is formed on the etching protection film 30. Then, the photoresist film is patterned so as to clear the regions of the groove portions 6 by the photolithography technique. Then, etching is performed using the patterned photoresist film as a mask, and the etching protection film 30 is selectively removed. After that, the photoresist film is removed. As a result, as shown in FIG. 9, the etching protection film 30 that has already been patterned can be patterned further in a state in which the regions of the groove portions 6 are cleared.

Next, the wafer S is etched using, as a mask, the etching protection film 30 that has been patterned again. After that, the etching protection film 30 used as the mask is removed. By doing this, as shown in FIG. 10, the groove portions 6 can be formed respectively in the both principal surfaces of the pair of vibrating arm portions 3 and 4.

Note that the plurality of piezoelectric plates 2 remain in a state in which they are connected to the wafer S via connection portions (not shown in the drawings) until a cutting step to be performed later is performed.

Electrode Forming Step

Next, an electrode forming step is performed in which an electrode film is patterned on the outer surfaces of the plurality of piezoelectric plates 2 by performing exposure through a mask (not shown in the drawings), thus forming the excitation electrodes 10 and 11, the lead-out electrode 16 and the mount electrodes 12 and 13 (S4). This step will be explained in more detail.

In the electrode forming step, first, as shown in FIG. 11, an electrode film 31 is formed by deposition, sputtering or the like on the outer surfaces of the piezoelectric plate 2 in which the groove portions 6 are formed (S4 a). Note that FIG. 11, FIG. 14 and FIG. 15 show only the one vibrating arm portion 3.

Next, a photoresist film forming step is performed in which a photoresist film (not shown in the drawings) is formed on the electrode film 31 (S4 b). The photoresist is a compound whose base is resin that has photosensitivity to ultraviolet light. A positive type photoresist is used in the present embodiment. Since the photoresist has fluidity, it is coated by spray coating or the like.

Next, as shown in FIG. 12, a first exposure step is performed in which the photoresist film (not shown in the drawings) is exposed to ultraviolet light using a mask 33 having a first opening 32 formed thereon (S4 c). At this time, sections where the electrode film 31 is to be left are patterned so that they are coated with the photoresist film (not shown in the drawings). A light shielding portion is formed on a section of the mask 33 where the photoresist film is to be left, and the first opening 32 is formed on a section of the mask 33 where the photoresist film is to be removed. Here, a section of the first opening 32 that corresponds to the clearance WO between the principal surface electrode portion 20 and the side surface electrode portion 21 is formed to have an opening width W1. Further, the first opening 32 is formed in a section P that corresponds to the fork portion 15 of the piezoelectric vibrating reed 1. Here, a section corresponding to the clearance U0 between the side surface electrode portion 21 formed on the inner side surface of the one vibrating arm portion 3 and the side surface electrode portion 21 formed on the inner side surface of the other vibrating arm portion 4 is formed to have an opening width U1.

FIG. 16A shows a state before the first exposure step and FIG. 16B shows a state after the first exposure step. A section (a C portion), where a photoresist film 36 is formed with a predetermined thickness, is exposed in the whole thickness direction by the first exposure step. However, a section (an A portion), where the photoresist film 36 is locally thick, is not exposed in the whole thickness direction by the first exposure step, and the photoresist film 36 is left.

Second Exposure Step

To address this, as shown in FIG. 13, a second exposure step is performed in which the photoresist film is further exposed to ultraviolet light using a correction mask 35 on which a second opening 34 is arranged (S4 d). The second opening 34 of the correction mask 35 is formed at a position where the second opening 34 overlaps with a part of the first opening 32 of the mask 33. First, the second opening 34 is formed in a section corresponding to the clearance W0 between the principal surface electrode portion 20 and the side surface electrode portion 21. An opening width W2 of the second opening 34 in this section is formed to be equal to or smaller than the opening width W1 of the first opening 32. It is desirable that the opening width W2 be equal to or more than 0.6 times and equal to or less than 0.7 times the opening width W1. Note that exposure conditions in the second exposure step are the same as those in the first exposure step.

FIG. 16C shows a state after the second exposure step and FIG. 16D shows a state after a development step, which will be described later. Even the section where the photoresist film 36 is locally thick is exposed in the whole thickness direction because a total exposure time is extended by the second exposure step. It is therefore possible to reliably remove the photoresist film of the section corresponding to the clearance WO between the principal surface electrode portion 20 and the side surface electrode portion 21. As a result, through a metal etching step to be described later, it is possible to secure the clearance W0 between the principal surface electrode portion 20 and the side surface electrode portion 21.

Generally, the interval between the groove portions 6 and the side surfaces of the vibrating arm portions 3 and 4 in the piezoelectric vibrating reed 1 is formed to be significantly narrow in order to suppress the R1 value to a low value. Therefore, the clearance WO between the principal surface electrode portion 20 formed in each of the groove portions 6 and the side surface electrode portion 21 formed in each of the side surfaces of the vibrating arm portions 3 and 4 becomes very narrow. In contrast to this, according to the piezoelectric vibrating reed manufacturing method of the present embodiment, it is possible to reliably inhibit a short circuit failure between the principal surface electrode portion 20 and the side surface electrode portion 21 in the clearance W0.

In addition, the opening width W2 of the second opening 34 of the correction mask 35 is formed to be equal to or less than the opening width W1 of the first opening 32 of the mask 33. Therefore, even if the total exposure time is extended by the second exposure step, an exposure range does not exceed the clearance W0. Therefore, it is possible to leave the photoresist film in regions where the principal surface electrode portion 20 and the side surface electrode portion 21 are to be formed. As a result, through the metal etching step to be described later, it is possible to form the principal surface electrode portion 20 and the side surface electrode portion 21 to have predetermined shapes. Thus, the R1 value can be suppressed to a low value.

Returning to FIG. 13, the second opening 34 is formed in a section P′ that corresponds to the fork portion 15 of the piezoelectric vibrating reed 1. More specifically, the second opening 34 is formed in the section corresponding to the clearance U0 between the side surface electrode portion 21 formed on the inner side surface of the one vibrating arm portion 3 and the side surface electrode portion 21 formed on the inner side surface of the other vibrating arm portion 4. An opening width U2 of the second opening 34 in this section is formed to be substantially the same as the opening width U1 of the first opening 32. Since the total exposure time is extended by performing the second exposure step using the correction mask 35, the whole of the photoresist film of the fork portion 15 is exposed. Therefore, it is possible to reliably remove the photoresist film of the fork portion 15. As a result, through the metal etching step to be described later, it is possible to secure the clearance U0 between the side surface electrode portion 21 formed on the inner side surface of the one vibrating arm portion 3 and the side surface electrode portion 21 formed on the inner side surface of the other vibrating arm portion 4.

Note that, in the vicinity of the fork portion 15, even if a removal amount of the electrode film becomes excessive, it does not affect characteristic values, more specifically, it does not increase the R1 value. Given this, if the opening width U2 of the second opening 34 is made substantially the same as the opening width U1 of the first opening 32 and the photoresist film of the fork portion 15 is removed, it is possible to more reliably inhibit a short circuit failure between the electrodes.

After the exposure, unnecessary portions are removed by developing fluid, and through a heating step etc., the photoresist film (not shown in the drawings) is solidified (S4 e). Then, through metal etching (S4 f), a photoresist pattern is formed by the photoresist film 36 having shapes corresponding to electrode forming sections as shown in FIG. 14. Then, by removing the photoresist film 36 (S4 g), the exciting electrodes 10 and 11, the lead-out electrode 16 and the mount electrodes 12 and 13 are formed as shown in FIG. 15 and the electrode forming step (S4) is ended.

Lastly, a cutting process is performed in which the connection portions (not shown in the drawings) used to connect the wafer S and the piezoelectric plates 2 are cut, and the plurality of piezoelectric plates 2 are thereby separated from the wafer S into small pieces (S5). Thus, the plurality of tuning fork type piezoelectric vibrating reeds 1 can be manufactured at one time from the single wafer S. At this point in time, the manufacturing step of the piezoelectric vibrating reed 1 is completed and the piezoelectric vibrating reed 1 shown in FIG. 1 is obtained.

As described above, in the piezoelectric vibrating reed manufacturing method according to the present embodiment, even if the thickness of the photoresist film formed in the photoresist film forming step becomes uneven and there is a section where the photoresist film is not sufficiently removed in the first exposure step, the opening width of the second opening 34 is equal to or less than the opening width of the first opening 32. It is therefore possible to sufficiently remove the photoresist film to be removed by the second exposure step without reducing a surface area of the photoresist film to be left. Accordingly, it is possible to inhibit a short circuit failure between the pair of electrodes.

Manufacturing Method of At-Cut Piezoelectric Vibrating Reed

The piezoelectric vibrating reed manufacturing method according to the present embodiment can also be applied to an AT-cut piezoelectric vibrating reed (hereinafter also referred to as an “AT vibrating reed”).

An AT vibrating reed 142 shown in FIG. 24 is provided with an oblong-shaped piezoelectric plate 149. A rectangular-shaped excitation electrode 140 is formed in a central portion of the piezoelectric plate 149. A pair of mounting electrodes 141 are formed at both end portions of one side of the piezoelectric plate 149. The excitation electrode 140 and the pair of mounting electrodes 141 are formed on both surfaces of the piezoelectric plate 149. The mounting electrodes 141 formed on the both surfaces are mutually connected by side surface electrodes 144 formed on a side surface of the piezoelectric plate 149. The pair of side surface electrodes 144 are arranged with a clearance TO interposed therebetween. The excitation electrode 140 formed on the top surface of the piezoelectric plate 149 is connected to one of the pair of mounting electrodes 141 and the excitation electrode 140 formed on the back surface of the piezoelectric plate 149 is connected to the other mounting electrode 141.

The first exposure step is performed using a mask 143 shown in FIG. 25. A first opening 146 is formed in the mask 143. The first opening 146 is formed such that a section corresponding to the clearance T0 between the pair of side surface electrodes 144 has an opening width T1. In the first exposure step, the photoresist film arranged on the side surface of the piezoelectric plate 149 is exposed through the opening width T1, and therefore there is a possibility that a part of the photoresist film arranged in the clearance T0 is left unexposed. In this case, the clearance TO between the pair of side surface electrodes 144 is connected and a short circuit failure occurs.

To address this, the second exposure step is performed using a correction mask 145 shown in FIG. 26. A second opening 147 is formed in the correction mask 145. The second opening 147 is formed in a section corresponding to the clearance TO between the pair of side surface electrodes 144. An opening width T2 of the second opening 147 in this section is formed to be substantially the same as the opening width T1 of the first opening 146. Note that there is a possibility that the photoresist film is also left on side surfaces of the piezoelectric plate 149 except the clearance T0. Therefore, the second opening 147 is also formed in sections corresponding to the side surfaces except the clearance T0.

The total exposure time is extended by performing the second exposure step using the correction mask 145. Therefore, all of the photoresist film arranged in the clearance TO between the pair of side surface electrodes 144 is exposed. It is therefore possible to reliably remove the photoresist film in the clearance T0. As a result, it is possible to secure the clearance T0 between the pair of side surface electrodes 144. Note that, in the clearance T0 between the pair of side surface electrodes 144, even if the removal amount of the electrode film becomes excessive, it does not affect characteristic values, more specifically, it does not increase the R1 value. Given this, if the opening width T2 of the second opening 147 is made substantially the same as the opening width T1 of the first opening 146 and the photoresist film of the clearance T0 is removed, it is possible to more reliably inhibit a short circuit failure between the pair of side surface electrodes 144.

Glass Packaged Piezoelectric Vibrator

Next, an embodiment of a piezoelectric vibrator according to the invention will be explained with reference to FIG. 17 to FIG. 20. Note that, in the present embodiment, a glass packaged piezoelectric vibrator of a surface mount type will be explained as an example of the piezoelectric vibrator.

As shown in FIG. 17 to FIG. 20, a piezoelectric vibrator 40 of the present embodiment has a box shape and is formed such that a base substrate 41 and a lid substrate 42 are laminated in two layers. The above-described tuning fork type piezoelectric vibrating reed 1 is housed in a cavity C formed inside the piezoelectric vibrator 40.

Note that FIG. 17 is an external perspective view of the piezoelectric vibrator 40. FIG. 18 is an internal structural diagram of the piezoelectric vibrator 40 shown in FIG. 17, and is a top view showing a state in which the lid substrate 42 is removed. FIG. 19 is a cross-sectional diagram of the piezoelectric vibrator 40 taken along a line D-D shown in FIG. 18. FIG. 20 is an exploded perspective view of the piezoelectric vibrator 40. Note that, in FIG. 20, each of the electrodes is omitted from the piezoelectric vibrating reed 1.

The piezoelectric vibrating reed 1 is mounted on an upper surface of the base substrate 41 by bump bonding, using bumps B made of gold or the like. More specifically, on the two bumps B that are formed on routing electrodes 48 and 49, to be described later, that are patterned on the upper surface of the base substrate 41, the pair of mount electrodes 12 and 13 are bump connected such that they are respectively in contact with the bumps B. Thus, the piezoelectric vibrating reed 1 is supported in a floating state above the upper surface of the base substrate 41, and at the same time, the mount electrodes 12 and 13 are respectively and electrically connected to the routing electrodes 48 and 49.

The lid substrate 42 is a transparent insulating substrate made of a glass material, for example, soda lime glass. As shown in FIG. 17, FIG. 19 and FIG. 20, the lid substrate 42 is formed in a plate shape. A rectangular-shaped recessed portion 42 a, in which the piezoelectric vibrating reed 1 is housed, is formed on a bonding surface side to which the base substrate 41 is bonded. When the base substrate 41 and the lid substrate 42 are overlapped with each other, the recessed portion 42 a forms the cavity C that houses the piezoelectric vibrating reed 1. The lid substrate 42 is anodically bonded to the base substrate 41 in a state in which the recessed portion 42 a faces the base substrate 41.

Similarly to the lid substrate 42, the base substrate 41 is a transparent insulating substrate made of a glass material, for example, soda lime glass. As shown in FIG. 17 to FIG. 20, the base substrate 41 is formed in a plate shape having a size that can be overlapped and aligned with the lid substrate 42.

A pair of through holes 43 and 44, which penetrate the base substrate 41, are formed in the base substrate 41. The pair of through holes 43 and 44 are formed such that they are arranged inside the cavity C. More specifically, the one through hole 43 is located on the base portion 5 side of the mounted piezoelectric vibrating reed 1, and the other through hole 44 is located on the tip end portion side of the vibrating arm portions 3 and 4.

Further, in the present embodiment, the through holes 43 and 44 that straightly pass through the base substrate 41 are used for explanation. However, the invention is not limited to this case. For example, the through holes 43 and 44 may be formed in a tapered shape such that their diameter gradually reduces toward a lower surface of the base substrate 41. In either case, it is sufficient if the through holes 43 and 44 penetrate the base substrate 41.

A pair of through electrodes 45 and 46 are formed in the pair of through holes 43 and 44 such that the through electrodes 45 and 46 fill up the through holes 43 and 44. The through electrodes 45 and 46 completely block the through holes 43 and 44 and maintain air-tightness in the cavity C. At the same time, the through electrodes 45 and 46 serve to achieve electrical connection between external electrodes 50 and 51, which will be described later, and the routing electrodes 48 and 49.

A bonding film 47 for anodic bonding and the pair of routing electrodes 48 and 49 are patterned on the upper surface side (a bonding surface side to which the lid substrate 42 is bonded) of the base substrate 41 using a conductive material (for example, aluminum). Among them, the bonding film 47 is formed along the peripheral edge of the base substrate 41 so as to surround the periphery of the recessed portion 42 a formed in the lid substrate 42.

Moreover, the pair of routing electrodes 48 and 49 are patterned such that one of the pair of through electrodes 45 and 46, the through electrode 45, is electrically connected to the one mount electrode 12 of the piezoelectric vibrating reed 1, and the other through electrode 46 is electrically connected to the other mount electrode 13 of the piezoelectric vibrating reed 1.

More specifically, as shown in FIG. 18 to FIG. 20, the one routing electrode 48 is formed directly above the one through electrode 45 to be located directly below the base portion 5 of the piezoelectric vibrating reed 1. Further, the other routing electrode 49 is formed to be located directly above the other through electrode 46 after being led out from a position adjacent to the one routing electrode 48 towards the tip end portion side of the vibrating arm portion 4 along the vibrating arm portion 4.

The bumps B are formed on the pair of routing electrodes 48 and 49, and the piezoelectric vibrating reed 1 is mounted using the bumps B. Thus, the one mount electrode 12 of the piezoelectric vibrating reed 1 is conductively connected to the one through electrode 45 via the one routing electrode 48, and the other mount electrode 13 is conductively connected to the other through electrode 46 via the other routing electrode 49.

Further, as shown in FIG. 17, FIG. 19 and FIG. 20, a pair of external electrodes 50 and 51, which are respectively and electrically connected to the pair of through electrodes 45 and 46, are formed on the lower surface of the base substrate 41. Thus, the pair of external electrodes 50 and 51 are electrically connected to the pair of excitation electrodes 10 and 11 of the piezoelectric vibrating reed 1 via the pair of through electrodes 45 and 46 and the pair of routing electrodes 48 and 49.

When the piezoelectric vibrator 40 structured in this manner is operated, a predetermined drive voltage is applied between the pair of external electrodes 50 and 51. Thus, a current can be applied to the excitation electrodes 10 and 11 of the piezoelectric vibrating reed 1, and the pair of vibrating arm portions 3 and 4 are allowed to vibrate at a predetermined frequency in a direction to move closer to or away from each other. This vibration can be used as the time source, the timing source of control signals, the reference signal source, and the like.

The piezoelectric vibrator 40 of the present embodiment includes the piezoelectric vibrating reed 1 which is unlikely to cause a short circuit between the electrodes and provides reliability for stable operation. It is therefore possible to achieve a high-quality piezoelectric vibrator having improved reliability.

Moreover, since the piezoelectric vibrator 40 is a glass-packaged piezoelectric vibrator of the surface mount type in which the piezoelectric vibrating reed 1 is airtightly sealed in the cavity C, it is possible to allow the piezoelectric vibrating reed 1 to vibrate without being affected by dust or the like, and it is possible to achieve high quality. In addition, since the piezoelectric vibrator 40 is a surface mount type piezoelectric vibrator, it can be mounted easily and has excellent stability after being mounted.

Oscillator

Next, an embodiment of an oscillator according to the invention will be explained with reference to FIG. 21.

In an oscillator 100 of the present embodiment, the above-described piezoelectric vibrator 40 is formed as an oscillation element that is electrically connected to an integrated circuit 101 as shown in FIG. 21. Note that the piezoelectric vibrator 40 may be incorporated.

The oscillator 100 is provided with a substrate 103 on which an electronic component 102 such as a capacitor is mounted. The above-described integrated circuit 101 for the oscillator is mounted on the substrate 103, and the piezoelectric vibrating reed 1 of the piezoelectric vibrator 40 is mounted in the vicinity of the integrated circuit 101.

The electronic component 102, the integrated circuit 101 and the piezoelectric vibrator 40 are respectively and electrically connected by wiring patterns, which are not shown in the drawings. Note that each of the structural components is molded by resin, which is not shown in the drawings.

In the oscillator 100 structured in this manner, when a voltage is applied to the piezoelectric vibrator 40, the piezoelectric vibrating reed 1 in the piezoelectric vibrator 40 vibrates. The vibration is converted to an electrical signal by a piezoelectric property of the piezoelectric vibrating reed 1, and input to the integrated circuit 101 as an electrical signal. The input electrical signal is subjected to various types of processing by the integrated circuit 101 and is output as a frequency signal. Thus, the piezoelectric vibrator 40 functions as an oscillation element.

Further, by selectively setting the structure of the integrated circuit 101, for example, to a real time clock (RTC) module or the like in response to demand, in addition to a single-function oscillator for a timepiece and the like, it is possible to add a function of controlling an operation date or time of the device or an external device or a function of providing time or a calendar.

The oscillator 100 of the present embodiment is provided with the above-described piezoelectric vibrator 40, and it is therefore possible to improve the reliability and quality of the oscillator 100 itself. In addition to this, stable and highly accurate frequency signals can be obtained over a long period of time.

Electronic Device

Next, an embodiment of an electronic device according to the invention will be explained with reference to FIG. 22. Note that a portable information device 110 having the above-described piezoelectric vibrator 40 will be explained as an example of the electronic device. Note that the piezoelectric vibrator 40 may be incorporated.

First, the portable information device 110 according to the present embodiment is represented by a mobile phone, for example, and is made by developing and improving a wrist watch in related art. The external appearance is similar to the wrist watch, and a liquid crystal display is arranged in a section corresponding to a dial plate so that current time and the like can be displayed on its screen. When being used as a communication device, it can be removed from the wrist, and communication similar to a mobile phone of related art can be performed using a speaker and a microphone incorporated in an inner side section of a band. However, as compared to the mobile phone of the related art, it is dramatically compact and lightweight.

Next, the structure of the portable information device 110 of the present embodiment will be explained.

As shown in FIG. 22, the portable information device 110 is provided with the piezoelectric vibrator 40 and a power supply portion 111 to supply electric power. The power supply portion 111 is formed by a lithium secondary battery, for example. A control portion 112 that performs various types of control, a time measuring portion 113 that counts time etc., a communication portion 114 that performs communication with the outside, a display portion 115 that displays various types of information, and a voltage detection portion 116 that detects a voltage of each of the functional portions are connected in parallel to the power supply portion 111. Electric power is supplied to each of the functional portions by the power supply portion 111.

The control portion 112 controls each of the functional portions and thereby performs operation control of an entire system 64, such as transmission and reception of audio data, measurement and display of current time, and the like. Further, the control portion 112 is provided with a ROM into which a program is written in advance, a CPU that reads and executes the program written into the ROM, a RAM that is used as a work area of the CPU, and the like.

The time measuring portion 113 is provided with an integrated circuit that incorporates an oscillation circuit, a register circuit, a counter circuit and an interface circuit etc., and the piezoelectric vibrator 40. When a voltage is applied to the piezoelectric vibrator 40, the piezoelectric vibrating reed 1 vibrates. The vibration is converted to an electrical signal due to piezoelectric property of crystal, and is input to the oscillation circuit as the electrical signal. The output of the oscillation circuit is binarized and measured by the register circuit and the counter circuit. Then, signal transmission and reception with the control portion 112 is performed via the interface circuit, and current time, current date or calendar information etc. is displayed on the display portion 115.

The communication portion 114 has similar functions to those of the mobile phone of the related art, and is provided with a wireless portion 117, an audio processing portion 118, a switching portion 119, an amplifier portion 120, an audio input/output portion 121, a telephone number input portion 122, a ring tone generation portion 123 and a call control memory portion 124.

The wireless portion 117 carries out transmission and reception of various types of data, such as audio data, with a base station via an antenna 125. The audio processing portion 118 encodes and decodes an audio signal input from the wireless portion 117 or the amplifier portion 120. The amplifier portion 120 amplifies a signal input from the audio processing portion 118 or the audio input/output portion 121 to a predetermined level. The audio input/output portion 121 is formed by a speaker, a microphone and the like, and makes a ring tone and incoming audio louder and collects audio.

The ring tone generation portion 123 generates a ring tone in response to a call from the base station. The switching portion 119 switches the amplifier portion 120 connected to the audio processing portion 118 to the ring tone generation portion 123 only when a call arrives, so that the ring tone generated in the ring tone generation portion 123 is output to the audio input/output portion 121 via the amplifier portion 120.

Note that the call control memory portion 124 stores a program relating to incoming and outgoing call control for communications. The telephone number input portion 122 includes, for example, numeric keys from 0 to 9 and other keys and the telephone number of a call destination is input by depressing these numeric keys and the like.

The voltage detection portion 116 detects a voltage drop and notifies the control portion 112 of it when a voltage applied by the power supply portion 111 to each of the functional portions, such as the control portion 112, drops below a predetermined value. The predetermined voltage value in this case is a value pre-set as the lowest voltage necessary to operate the communication portion 114 stably, and is, for example, about 3V. When receiving a notification of the voltage drop from the voltage detection portion 116, the control portion 112 disables operations of the wireless portion 117, the audio processing portion 118, the switching portion 119 and the ring tone generation portion 123. In particular, it is essential to stop the operation of the wireless portion 117 that consumes a large amount of electric power. Furthermore, a message informing that the communication portion 114 is unavailable due to insufficient battery power is displayed on the display portion 115.

More specifically, it is possible to disable the operation of the communication portion 114 by the voltage detection portion 116 and the control portion 112, and to display the notification message on the display portion 115. Although a character message may be used for this display, an x (cross) mark may be put on a telephone icon displayed on an upper section of a display screen of the display portion 115, as a more intuitive display.

Note that, by providing a power supply shutdown portion 126 that is capable of selectively shutting down the power supply to portions involved with the function of the communication portion 114, it is possible to stop the function of the communication portion 114 in a more reliable manner.

The portable information device 110 of the present embodiment is provided with the above-described piezoelectric vibrator 40. Therefore, it is possible to improve the reliability and quality of the portable information device itself. In addition to this, it is possible to display stable and highly accurate timepiece information over a long period of time.

Radio Timepiece

Next, an embodiment of a radio timepiece 130 according to the invention will be explained with reference to FIG. 23. The radio timepiece 130 of the present embodiment is provided with the piezoelectric vibrator 40 that is electrically connected to a filter portion 131 as shown in FIG. 23, and is a timepiece that has a function of receiving a standard wave including timepiece information, and a function of automatically correcting the standard wave to a correct time and displaying it. Note that the piezoelectric vibrator 40 may be incorporated.

In Japan, transmitting stations (transmitter stations) for transmitting standard waves are located in Fukushima prefecture (40 kHz) and Saga prefecture (60 kHz), and transmit standard waves, respectively. A long wave corresponding to 40 kHz or 60 kHz has a property of propagating on the ground surface and also has a property of propagating while being reflected by an ionized layer and the ground surface. Accordingly, the propagation range is wide and the above-mentioned two transmitting stations cover the entire area of Japan.

Hereinafter, a functional structure of the radio timepiece 130 will be explained in detail.

An antenna 132 receives a standard wave that is a long wave of 40 kHz or 60 kHz. The standard wave, which is a long wave, is a wave that is obtained by performing AM modulation of time information, which is called a time code, on a carrier wave of 40 kHz or 60 kHz. The received standard wave, which is a long wave, is amplified by an amplifier 133, and is filtered and tuned by the filter portion 131 having a plurality of the piezoelectric vibrators 40.

The piezoelectric vibrators 40 of the present embodiment are respectively provided with crystal oscillator portions 138 and 139 having resonance frequencies of 40 kHz and 60 kHz, which are the same as the above-described carrier frequencies.

Further, the filtered signal with a predetermined frequency is detected and demodulated by a detection and rectification circuit 134. Then, the time code is taken out through a waveform shaping circuit 135 and is counted by a CPU 136. The CPU 136 reads information of a current year, cumulative days, a day of the week, a time of day, and the like. The read information is reflected on an RTC 137 and correct time information is displayed.

Since the carrier wave is 40 kHz or 60 kHz, the above-described oscillator having a tuning-fork type structure is preferably used as the crystal oscillator portions 138 and 139.

Note that, although the above-described explanation is made using an example in Japan, the frequencies of long wave standard waves are different in overseas countries. For example, the standard wave with a frequency of 77.5 kHz is used in Germany. Accordingly, when the radio timepiece 130 that is also compatible in overseas countries is incorporated into a portable device, the piezoelectric vibrator 40 having a frequency different from the frequency used in Japan is further necessary.

The radio timepiece 130 of the present embodiment is provided with the above-described piezoelectric vibrator 40. Therefore, it is possible to improve the reliability and quality of the radio timepiece itself. In addition to this, it is possible to count time stably and highly accurately over a long period of time.

Note that the technological scope of the invention is not limited to the above-described embodiments, and various modifications can be made within a scope that does not depart from the spirit of the invention.

For example, although in the above-described embodiments, the tuning fork type piezoelectric vibrating reed 1 and the AT-cut piezoelectric vibrating reed are used as examples, another piezoelectric vibrating reed can also be manufactured using the piezoelectric vibrating reed manufacturing method according to the invention. 

1. A method of manufacturing piezoelectric vibrating reeds comprising: forming an electrode film on a piezoelectric reed; forming a photoresist film on the electrode film formed on the piezoelectric reed; photographically removing part of the photoresist film with a first mask having a first strip pattern which defines a first in-between distance substantially equal to a distance between adjacent electrodes to be formed from the electrode film; photographically exposing the partially removed photoresist film with a second mask having a second strip pattern co-extensive with the first strip pattern exposed by the first mask on the photoresist film, wherein the second strip pattern is narrower than the first strip pattern; and photographically removing part of the electrode film formed on the piezoelectric reed according to a pattern of the photoresist film removed by the first and second masks.
 2. The method according to claim 1, wherein the first and second masks have second and third strip patterns, respectively, which are coextensive with each other and substantially equal in width.
 3. The method according to claim 2, wherein the piezoelectric reed is a of a tuning-fork type which has a base and a pair of arms extending from the base, and the second the third strip patterns lie on the base between the arms near proximal ends of the arms.
 4. The method according to claim 1, wherein the piezoelectric reed is an AT-cut piezoelectric reed. 